Hi everyone,

I apologize in advance for what is almost certainly going to be a lengthy
post. The recent events, specifically involving C/2010 X1 and observations
of it, have prompted me to write this, but this also strikes me as a good
opportunity to comment on issues and trends that have led up to the recent
events. As a faithful observer of comets for over four decades I'd like to
think I've earned a right to address these issues.

First off, of course, there is now no doubt that a faint dust stream remnant
of C/2010 X1 does indeed continue to exist. I was certainly skeptical of
this, up until the time I saw Rolando Ligustri's image that he took on the
22nd; but that image, and the other images that he and other observers have
taken since then, clearly demonstrate that this dust stream is there. I
rather agree with John Bortle's comparison to the "head-less" Kreutz
sungrazer of 1887; one other example that occurred to me (although the
physical circumstances are obviously different) is the recent P/2010 A2.

It so happened that Rolando took his October 22 image at the precise time
that I was making an unsuccessful visual attempt for this comet.
Accordingly, as soon as I saw the image I noticed that there was nothing at
the ephemeris position of the comet itself; the closest relatively bright
portion of the "tail" (which is how I will refer to it from here on) was
displaced several arcminutes to the west-northwest of the ephemeris
position. I had concentrated my search efforts on the ephemeris position,
and thus I should *not* have seen anything when I was making my search. I
verified this displacement with the image that Rolando took the following
morning.

Armed with this knowledge, and also the knowledge of what precisely to look
for, I made another attempt on the morning of October 24. I did in fact seem
to see a shapeless but extended "something" in about the expected position,
and moreover this "something" seemed to move westward at the expected rate.
This was an extreme borderline observation, however, and was akin to some of
the very extended diffuse nebulae I've occasionally looked for (the
supernova remnant S147 in Auriga/Taurus being an example); I could "see"
something by detecting the very slight differences in the background sky
brightness between the locations where it "was" and where it "wasn't."

For what it's worth, I did attempt a brightness measurement by an extreme
defocusing of stars, and would say somewhere around m1 ~12: I agree with
John, though, that this is essentially meaningless -- for one thing, there
is no coma, and that is usually what is meant by a comet's brightness -- and
at best it refers to a shapeless, ill-defined portion of the tail remnant.

I had to be out of town for a family emergency on the morning of the 25th
(and I think it was cloudy here anyway), but I tried again this morning (the
26th). Again, I seemed to see this extremely faint "something" that moved in
the right direction at the right rate, and, again, it was an extreme
borderline observation. At this point I am reasonably sure that I have
indeed detected this tail remnant of C/2010 X1 on the two mornings in
question, although I would greatly appreciate it if anyone who was imaging
the comet on those dates, and especially around the times of my observations
(roughly 8:30 to 9:30 UT on October 24, 7:50 to 8:50 UT on October 26) could
either send those images to me, or post them somewhere.


Now, having reported all this, I would like to comment on some visual
cometary observations, not only of C/2010 X1 but some other comets, and in
general. While Juan Gonzalez has been a bit on the "hot seat" with his
reports of C/2010 X1 -- and I freely admit that I have been among his
doubters, and I will get to that in a moment -- my comments are directed
more towards the current community of comet observers in general. I will
occasionaly use the word "you," but, except in the specific case of the
recent observations of C/2010 X1, I am not referring to any observer in
particular.

Before proceeding, I wish to reiterate something I said in an earlier post,
i.e., at no time do I mean anything personal about any individual. I
consider everyone here friends and colleagues, and I have high respect for
all of you. I am speaking strictly of the scientific observations involved,
as I would like to believe that the visual brightness (and morphology)
reports of comets continue to have scientific value. That requires, though,
that they be done correctly at all times.

Let's look at Juan's two recent reports of C/2010 X1. The first one, on
October 9, specifically refers to a "coma;" we now know that there is no
"coma" for this comet, and anything that might have been visible was not at
the ephemeris position, and Juan makes no mention of this. Furthermore, he
remarks that there was zodiacal light present (with which I will concur,
with my own unsuccessful observation attempt around that same time), and,
considering the extremely low surface brightness of the "tail remnant," any
kind of background lighting should have wiped it out completely. (Recall
that all the CCD images at that time showed nothing, or at best, an
extremely faint and uncertain fragment that may or may not have been real.)
And while I accept at face value Juan's comments about the clarity of the
atmosphere down to the horizon, at an altitude of 23 degrees you are still
looking through over 2.5 air masses, and you are going to be encountering a
non-trivial amount of extinction.

The second observation, on October 21, does seem at face value to be
reasonably consistent with what the later images showed, although I note
that he reported one of his "bright areas" to be at the ephemeris position.
There would have been no zodiacal light at the time of the observation,
although the reported altitude of 16 degrees works out to over 3.5 air
masses and thus a significant amount of extinction; if this was at the
beginning of the observation (Juan doesn't say, but does report that he
followed his object for 40 minutes) then the extinction would obviously have
decreased throughout the observation.

For the record, the altitude at the beginning times of my two recent
observatons was 44 degrees (1.4 air masses) on both mornings. I was using a
41 cm Newtonian, with a fairly fast optical system (f/4.5); I again note
that while I am reasonably certain of my sightings (although perhaps not
100% certain until/unless I can see some images taken around then), these
were extreme borderline detections.

The upshot here is that I must remain very skeptical of the October 9 report
as, all things considered, it is inconsistent with what the CCD images (both
then and now) have revealed. The October 21 report is much less clear to me;
I do have some problems with it, which I've discussed, but on the other hand
it is consistent enough with the CCD images that I cannot simply dismiss it.
"Benefit of the doubt" would suggest that I accept it as a positive
observation, but to be honest, I don't believe I can go either way at this
time. The best I can do right now is consider it an open issue, which I may
never be able to resolve to my complete satisfaction either way. (This
definitely is not the first such "open issue" I have encountered over the
years . . . )


But to turn now to the issues which have contributed to the difficulties I
have had with some of the reported observations (and, reminder, from here on
"you" is generic):

In addition to my one comet discovery, during the days before the web and
the NEOCP I was constantly being called or e-mailed by Dan Green or Brian
Marsden to confirm various comet discoveries, and over a period of about two
decades I successfully confirmed numerous such discoveries (as well as
dis-confirmed numerous other reports). One of the comets I confirmed was as
faint as m1=13.5. Some of the comets were several degrees away from their
"expected" locations, and yet I was still able to track them down (and
perhaps it's worth keeping in mind that we were not even sure these comets
were real, although we considered some more likely than others).

While I am not infallible, with this kind of track record it is
inconceivable to me that I could be looking *directly* at a 9th- or
10th-magnitude comet, and *not* see it. Yet, if I am to believe some of the
reports that have been submitted in recent years, that is precisely the
case. There are several examples I can cite, but I will focus on two recent
ones.

We've already discussed C/2011 M1 to an extent. Some of you were
consistently reporting this comet to be as bright as m1 ~9-10, with a large,
diffuse coma, and yet, despite numerous search attempts, I never saw it. And
in this case, the CCD images backed me up:

With a telescope of any size, a CCD image with an exposure time of only 15
or 20 seconds will reveal stars fainter than what can be visually detected
with that telescope. In the case of the C/2011 M1 images, the total exposure
times were in the range of 16 *minutes* -- and yet, they only revealed an
extremely faint smudge of light on the verge of complete disintegration that
was barely detectable.

Another example that I have not seen discussed here yet is C/2011 A3. Again,
several of you have reported this comet as being bright at m1 ~9-10 and with
a large coma, and, again, despite numerous attempts I have failed to see it.
(Other observers have privately informed me that they, too, have failed to
see it.) Once again, the CCD images back me up: even when processed with an
unreasonably high contrast, they show only a small and relatively condensed
coma that is no brighter than the 15th-magnitude stars in the field (an
appearance, incidentally, that is entirely consistent with a comet that is
2.5 to 3 AU from both the earth and the sun).

These are *not* cases of "visual photometry vs. CCD photometry;" these are
cases of CCD images showing what is and what isn't there. It is very
disingenuous to cite the CCD images as positive evidence of the C/2010 X1
observations, and then turn around and dismiss the CCD images of C/2011 M1
and C/2011 A3 which reveal that those two comets were much, much fainter
than the visual reports at the times in question.


There are two other issues I would like to touch upon. Back when they were
active, I was constantly cross-checking my observations against those of
John Bortle and Charles Morris, and I was almost always within a
half-magnitude or so of their reports. This doesn't necessarily mean that
any particular individual is "right," and, yes, we all should "call them as
we see them," but if everyone involved is doing it correctly, we should all
be seeing something fairly similar to each other. After all, if the depth of
a lake is 10 meters at a certain point, then all measurements of the depth
at that point should be somewhere close to 10 meters. Similarly, if a
comet's "true" brightness is magnitude 10.0, then all measurements should be
somewhat close to that (say, between magnitude 9.5 and 10.5).

But I am not seeing that now; I am seeing reported brightnesses that are
two, three, sometimes more magnitudes different from what I am seeing.
Again, I am not saying that my measurements are always "right," but I find
it hard to believe that I've lost my ability to make reasonably accurate
measurements within the past decade. It's like we're back to those depth
measurements; if one person is reporting a depth of 2 meters, while someone
else is reporting a depth at the same point of 28 meters, something is
wrong. Likewise for our 10th-magnitude comet; if one observer reports it at
7th magnitude, and another observer at 13th magnitude, something is wrong.

And then, there is the topic of limiting cometary magnitudes for telescopes
of various apertures. I have been utilizing the 41 cm telescope for over two
decades now, and can state with reasonable confidence that its limiting
magnitude for comets is around 14.5. (I'm referring to "cometary" comets,
not completely stellar ones, which I can obviously detect fainter.) Over the
years, observers I know with similar-sized telescopes have reported
something similar, and those with smaller or larger telescopes have reported
limiting magnitudes that are consistent with this.

And yet nowadays, I am seeing some of you, including some of you with
telescopes significantly smaller than mine, routinely reporting comet
magnitudes up to a full magnitude -- sometimes even more -- fainter than the
limit of my telescope. How is this possible? I think I've already shared the
story of the occasion where, by examining CCD images that I took almost
simultaneously with a faint comet I was attempting visually, I was able to
detect a comet at m1=14.8 -- but this took four nights (and two hours each
night) of this simultaneous visual/CCD work before I could finally convince
myself that that tiny speck of light that flickered at the extreme limit of
vision was indeed the comet I was after. Yet someone with a telescope
smaller than mine easily detects comets a full magnitude fainter than that??

A question I would ask is, do you ever look for a comet and *not* see it? If
you're constantly looking for comets near the limit of your telescope, there
should be quite a few of them that you never see. If you somehow are able to
"see" every comet you attempt, then I submit that something is wrong. You
all know how many comets I have visually observed over the years, but you
may not know that there are over 200 other comets that I have looked for,
and *not* seen.

I guess I am reminded of the old story of the "boy who cried 'wolf.'" If you
consistently report 9th-magnitude comets that aren't there, report comet
brightnesses that are three magnitudes different from what I'm seeing, and
report seeing comets with a small telescope that are far too faint for me to
see with my larger telescope, then you will have to pardon my skepticism
when it comes to reports of extremely unusual cometary phenomena like what
we've recently seen with C/2010 X1. Even if you got it right this time . . .

The enthusiasm for visual comet observations that I am seeing now is
refreshing to see, and again, I really would like to think that the data we
obtain is scientifically useful. (It might even help in resolving the
"visual photometry vs. CCD photometry" issue, although I sometimes think
that's an unsolvable problem.) But it can only be useful if it's done right.
I implore everyone here -- veterans included, and that includes me -- to be
careful and cautious in obtaining these observations, and to see to it that
we are making the most reliable observations that we can possibly make.


Sincerely,

Alan